As you can see in this website there is to much main menu voices (and the Main Menu takes up too much space) so I want group some voices as sub voices into a main voices.

I want something like this Joomla Main Menu: http://lnx.erusma.org/en/ in which, for example, if you pass the mouse on the Who We Are voice you can say the subvoice. Can I do the same thing in WP? (I do not want to associate the main voice to a specific page to a category, this simply must be not clickable)